ABSTRACT Composite sandwich structures are finding increasing applications in various fields and industries such as aerospace, automotive, acoustics and so on due to their high strength-to-weight ratio and better insulation properties. To facilitate the assembly of these structures, fasteners are employed, and drilling is one of the secondary manufacturing processes that can produce cost-effective and good-quality holes for fastening. This paper deals with characterising the quality of the drilled holes in glass fibre-reinforced plastic-polyurethane foam sandwich structures. This experiment has been designed using Taguchi’s L9 orthogonal array. The results indicate that smaller drill diameter and lower feed rate produce delamination of lower magnitude at entry and exit while higher spindle speeds followed by lower feed rates produced holes with minimal deviation from the ideal form.